It is a common desire to enhance images acquired from imaging devices to improve their image quality. There are fundamental attributes that govern the image quality of a grayscale image. These attributes are the brightness of an image, the dynamic range of an image, the contrast of detail in an image (or detail contrast), the sharpness of edges in an image, and the appearance of noise in an image. It is beneficial to provide a system that enables direct and independent control of these attributes of image quality. Further a system, which enables the control of the detail contrast, sharpness, and noise appearance in a density dependent fashion is also beneficial.
U.S. Pat. No. 5,805,721, inventors P. Vuylsteke and E. Schoeters, entitled “Method and Apparatus for Contrast Enhancement”, issued Sep. 8, 1998 describes a multi-resolution method for enhancing contrast with increased sharpness that includes dynamic range compression, and enhancing contrast without remarkably boosting the noise component. The described invention enhances detail contrast and sharpness via a multi-resolution method and controls dynamic range compression with a gradation curve to map the processed image into the appropriate dynamic range for the display. Application of the gradation curve will impact both the apparent detail contrast and dynamic range of the displayed image. Hence, both the modifying functions of the multi-resolution processing and the shape of the gradation curve affect the detail contrast in the image. This requires that both be adjusted when setting the detail contrast in the image.
U.S. Pat. No. 5,978,518, inventors Oliyide et al., entitled “Image Enhancement in Digital Image Processing”, issued Nov. 2, 1999 and U.S. Pat. No. 6,069,979 (continuation-in-part of U.S. Pat. No. 5,978,518), inventor VanMetter, entitled “Method for Compressing the Dynamic Range of Digital Projection Radiographic Images”, issued May 30, 2000, describe a multi-resolution method for performing dynamic range modification and high-frequency enhancement (including detail contrast). The methods include a tone scale look-up-table that is used to map the image for display rendering. A tone scale look-up-table impacts the dynamic range and contrast of detail in an image. Hence, in this method, the dynamic range and detail contrast of the image depends on both the settings of the frequency modification and the parameters of the tone scale look-up table. It is desirable, instead to have a single set of parameters that control these attributes independently.
U.S. Pat. No. 6,072,913, inventor M. Yamada, entitled “Image Processing Method and Apparatus”, issued Jun. 6, 2000, describes a multi-resolution method for enhancing frequencies with dynamic range compression. The described invention requires the definition of many functions to control the performance of the algorithm. It does not disclose a set of parameters that directly and independently control all of the fundamental attributes of image quality.
Thus, there is a need for a method that can be applied to an image, the parameters of which provide direct and independent control of the above stated fundamental attributes of image quality.